arXiv subjects

Z. Y. Zhang

Publications and source records attributed to Z. Y. Zhang.

70 records · Page 4Linked to original sources

arXiv2005

N phi state in chiral quark model

The structures of N phi states with spin-parity J^{p}=3/2^- and J^p=1/2^- are dynamically studied in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the baryon ground states, the binding energy of the deuteron, the nucleon-nucleon (NN) scattering phase shifts, and the hyperon-nucleon (YN) cross sections. The channel coupling of N phi and Lambda K* is considered, and the effect of the tensor force which results in the mixing of S and D waves is also investigated. The results show that the N phi state has an attractive interaction, and in the extended chiral SU(3) quark model such an attraction plus the channel coupling effect can consequently make for an N phi quasi-bound state with several MeV binding energy.

nucl-th↗

arXiv2005

Kaon-nucleon interaction in the extended chiral SU(3) quark model

The chiral SU(3) quark model is extended to include the coupling between the quark and vector chiral fields. The one-gluon exchange (OGE) which dominantly governs the short-range quark-quark interaction in the original chiral SU(3) quark model is now nearly replaced by the vector-meson exchange. Using this model, the isospin I=0 and I=1 kaon-nucleon S, P, D, F wave phase shifts are dynamically studied by solving the resonating group method (RGM) equation. Similar to those given by the original chiral SU(3) quark model, the calculated results for many partial waves are consistent with the experiment, while there is no improvement in this new approach for the P_{13} and D_{15} channels, of which the theoretical phase shifts are too much repulsive and attractive respectively when the laboratory momentum of the kaon meson is greater than 300 MeV.

nucl-th↗

arXiv2005

Coupled-channels study of Lambda K and Sigma K states in the chiral SU(3) quark model

The $S$-wave $ΛK$ and $ΣK$ states with isospin $I=1/2$ are dynamically investigated within the framework of the chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a good description of the energies of the baryon ground states, the binding energy of the deuteron, and the experimental data of the nucleon-nucleon ($NN$) and nucleon-hyperon ($NY$) scattering. Assumed not to give important contributions in the scattering processes, the s-channel quark-antiquark ($q\bar q$) annihilation interactions are not included as a first step. The results show a strong attraction between $Σ$ and $K$, which consequently results in a $ΣK$ quasi-bound state with about 17 MeV binding energy, unlike the case of $ΛK$ which is unbound. When the channel coupling of $ΛK$ and $ΣK$ is considered, a sharp resonance state near 1670 MeV with spin-parity $J^P=1/2^-$ is found. The narrow gap of the $ΛK$ and $ΣK$ thresholds, the strong attraction between $Σ$ and $K$, and the sizeable off-diagonal matrix elements of $ΛK$ and $ΣK$ are responsible for the appearance of this resonance.

hep-ph↗

arXiv2005

Further study on 5q configuration states in the chiral SU(3) quark model

The structure of the $5q$ configuration states with strangeness ${\cal{S}}=+1$ is further studied in the chiral SU(3) quark model based on our previous work. We calculate the energies of fifteen low configurations of the $5q$ system, four lowest configurations of $J^π={1/2}^-$ with $4q$ partition $[4]_{orb}(0s^4)[31]^{σf}$, four of $J^π={1/2}^+$ with $4q$ partition $[31]_{orb}(0s^30p)[4]^{σf}$ and seven of $J^π={1/2}^+$ with $4q$ partition $[4]_{orb}(0s^30p)[31]^{σf}$. Some modifications are made in this further study, i.e., the orbital wave function is extended as an expansion of 4 different size harmonic oscillator forms; three various forms (quadratic, linear and error function form) of the color confinement potential are considered; the states with $4q$ partition $[4]_{orb}(0s^30p)[31]^{σf}$ are added, which are unnegligible in the $J^π={1/2}^+$ case and were not considered in our previous paper, further the mixing between configurations $[31]_{orb}(0s^30p)[4]^{σf}$ and $[4]_{orb}(0s^30p)[31]^{σf}$ is also investigated. The results show that the T=0 state is still always the lowest one for both $J^π={1/2}^-$ and $J^π={1/2}^+$ states, and $J^π={1/2}^-, T=0$ state is always lower than that of $J^π={1/2}^+$. All of these modifications can only offer several tens to hundred MeV effect, and the theoretical value of the lowest state is still about 245 MeV higher than the experimental mass of $Θ^+$. It seems to be difficult to get the calculated mass close to the observed one with the reasonable parameters in the framework of the chiral SU(3) quark model when the model space is chosen as a $5q$ cluster.

nucl-th↗

arXiv2005

S, P, D, F wave KN phase shifts in the chiral SU(3) quark model

The $S$, $P$, $D$, $F$ wave $KN$ phase shifts have been studied in the chiral SU(3) quark model by solving a resonating group method equation. The numerical results of different partial waves are in agreement with the experimental data except for the cases of $P_{13}$ and $D_{15}$, which are less well described when the laboratory momentum of the kaon meson is greater than 400 MeV.

nucl-th↗

arXiv2005

N K and Delta K states in the chiral SU(3) quark model

The isospin I=0 and I=1 kaon-nucleon $S$, $P$, $D$, $F$ wave phase shifts are studied in the chiral SU(3) quark model by solving the resonating group method (RGM) equation. The calculated phase shifts for different partial waves are in agreement with the experimental data. Furthermore, the structures of the $ΔK$ states with L=0, I=1 and I=2 are investigated. We find that the interaction between $Δ$ and $K$ in the case of L=0, I=1 is attractive, which is not like the situation of the $NK$ system, where the $S$-wave interactions between $N$ and $K$ for both I=0 and I=1 are repulsive. Our numerical results also show that when the model parameters are taken to be the same as in our previous $NN$ and $YN$ scattering calculations, the $ΔK$ state with L=0 and I=1 is a weakly bound state with about 2 MeV binding energy, while the one with I=2 is unbound in the present one-channel calculation.

nucl-th↗

arXiv2004

Resonating group method study of kaon-nucleon elastic scattering in the chiral SU(3) quark model

The chiral SU(3) quark model is extended to include an antiquark in order to study the kaon-nucleon system. The model input parameters $b_u$, $m_u$, $m_s$ are taken to be the same as in our previous work which focused on the nucleon-nucleon and nucleon-hyperon interactions. The mass of the scalar meson $σ$ is chosen to be 675 MeV and the mixing of $σ_0$ and $σ_8$ is considered. Using this model the kaon-nucleon $S$ and $P$ partial waves phase shifts of isospin I=0 and I=1 have been studied by solving a resonating group method (RGM) equation. The numerical results of $S_{01}$, $S_{11}$, $P_{01}$, $P_{03}$, and $P_{11}$ partial waves are in good agreement with the experimental data while the phase shifts of $P_{13}$ partial wave are a little bit too repulsive when the laboratory momentum of the kaon meson is greater than 500 MeV in this present calculation.

nucl-th↗

arXiv2004

The Short Range Mechanism of N-N interaction in the Extended Chiral SU(3) Quark Model

We give the comparisons between the chiral SU(3) quark model and the extended chiral SU(3) quark model. The results show that the phase shifts of NN scattering are very similar. However, the short range mechanisms of nucleon-nucleon interaction are totally different. In the chiral SU(3) quark model, the short range interaction is dominantly from OGE, and in the extended chiral SU(3) quark model, it is dominantly from vector meson exchanges.

nucl-th↗

arXiv2004

N-N Interactions in the Extended Chiral SU(3) Quark Model

The chiral SU(3) quark model is extended to include coupling between vector chiral field and quarks. By using this model, the phase shifts of NN scattering for different partial waves are studied. The results are very similar to those of the chiral SU(3) quark model calculation, in which one gluon exchange (OGE) plays dominate role in the short range part of the quark-quark interactions. Only in the $^1S_0$ case, the one channel phase shifts of the extended chiral SU(3) quark model are obviously improved.

nucl-th↗

arXiv2003

A study of pentaquark $Θ$ state in the chiral SU(3) quark model

The structure of the pentaquark state uudd-sbar is studied in the chiral SU(3) quark model as well as in the extended chiral SU(3) quark model, in which the vector meson exchanges are included. Four configurations of JP=1/2- and four of JP=1/2+ are considered. The results show that the isospin T=0 state is always the lowest one for both JP=1/2- and JP=1/2+ cases in various models. But the theoretical value of the lowest one is still about 200-300 MeV higher than the experimental mass of $Θ$. It seems that a dynamical calculation should be done for the further study.

hep-ph↗

arXiv2001

Diomega production in relativistic heavy ion collisions

Using a multiphase transport model, we study the production of a new strange dibaryon (ΩΩ)_{0+} in dense hadronic matter formed in relativistic heavy ion collisions. The (multi-)strange baryons (Ξand Ω) are produced by strangeness-exchange reactions between antikaons and hyperons in the pure hadronic phase. The rescattering between the omegas at midrapidity leads to a production probability of \simeq 3x10^{-7} (ΩΩ)_{0+} per event at the RHIC energy of \sqrt s=130A GeV. The production probability would be enhanced by two orders of magnitude if (ΩΩ)_{0+} and omega reach chemical equilibrium during heavy ion collisions. We further find that the yield of (ΩΩ)_{0+} increases continuously from SPS to the highest RHIC energy.

nucl-th↗

arXiv2000

Possible S-wave Dibaryons in SU(3) Chiral Quark Model

In the framework of the SU(3) chiral quark model, the $S-$wave baryon-baryon bound states are investigated. It is found that according to the symmetry character of the system and the contributions from chiral fields, there are three types of bound states. The states of the first type, such as $[ΩΩ]_{(0,0)}$ and $[Ξ^{*}Ω]_{(0,1/2)}$ are deeply bound dibaryon with narrow widths. The second type states, $[Σ^{*} Δ]_{(0,5/2)}$,$[Σ^{*} Δ]_{(3,1/2)}$, $[ΔΔ]_{(0,3)}$ and $[ΔΔ]_{(3,0)}$ are also bound states, but with broad widths. $[ΞΩ- Ξ^{*}Ω]_{(1,1/2)}$, $[ΞΞ]_{(0,1)}$, and $[N Ω]_{(2,1/2)}$ are third type states. They, like {\em d}, are weakly bound only if the chiral fields can provide attraction between baryons.

nucl-th↗

arXiv2000

Dibaryon Systems In SU(3) Chira Quark Model

The possible candidates of $S-$wave dibaryons with various strange numbers are studied under the chiral SU(3) quark model. It is shown that there are three types of baryon-baryon bound states. The states of the first type are called deuteron-like states. If chiral fields can provide enough attraction between interacting baryons, these systems, such as $[ΞΩ- Ξ^{*}Ω]_{(1,1/2)}$, $[ΞΞ]_{(0,1)}$, $[N Ω]_{(2,1/2)}$ would be weakly bound. The states of the second type such as $[Σ^{*} Δ]_{(0,5/2)}$, $[Σ^{*} Δ]_{(3,1/2)}$, $[ΔΔ]_{(0,3)}$ and $[ΔΔ]_{(3,0)}$ are named as $ΔΔ$-like states. Due to the highly symmetric character in orbital space, these systems could be relatively deeply bound, but the strong decay modes of composed baryons cause the widths of the states much broader. The states of the third type are entitled as $ΩΩ$-like states. Due to the same symmetry character shown in the systems of the second type and the only weak decay mode of composed baryons, for instance in $[ΩΩ]_{(0,0)}$, or at most one strong decay mode of composed baryons, for example in $[Ξ^{*}Ω]_{(0,1/2)}$, these states are deeply bound states with narrow widths. The states of latter two types are most interesting new dibaryon states and should be carefully investigated both theoretically and experimentally.

nucl-th↗

arXiv1999

H-Dihyperon in Quark Cluster Model

The H dihyperon (DH) is studied in the framework of the SU(3) chiral quark model. It is shown that except the $σ$ chiral field, the overall effect of the other SU(3) chiral fields is destructive in forming a stable DH. The resultant mass of DH in a three coupled channel calculation is ranged from 2225 $MeV$ to 2234 $MeV$.

nucl-th↗

arXiv1999

Deltaron Dibaryon Structure in Chiral SU(3) Quark Model

We discuss the structure of Deltaron dibaryon in the chiral SU(3) quark model. The energy of Deltaron is obtained by considering the coupling of the $ΔΔ$ and $CC$ (hidden color) channels. The effects of various parameters on the Deltaron mass are also studied. It is shown that the mass of Deltaron is lower than the mass of $ΔΔ$ but higher than the mass of $ΔN π$.

nucl-th↗

arXiv1998

Chiral patterns arising from electrostatic growth models

Recently, unusual and strikingly beautiful seahorse-like growth patterns have been observed under conditions of quasi-two-dimensional growth. These `S'-shaped patterns strongly break two-dimensional inversion symmetry; however such broken symmetry occurs only at the level of overall morphology, as the clusters are formed from achiral molecules with an achiral unit cell. Here we describe a mechanism which gives rise to chiral growth morphologies without invoking microscopic chirality. This mechanism involves trapped electrostatic charge on the growing cluster, and the enhancement of growth in regions of large electric field. We illustrate the mechanism with a tree growth model, with a continuum model for the motion of the one-dimensional boundary, and with microscopic Monte Carlo simulations. Our most dramatic results are found using the continuum model, which strongly exhibits spontaneous chiral symmetry breaking, and in particular finned `S' shapes like those seen in the experiments.

cond-mat↗